Prince William needs to stop traveling with his entire family. That’s how they end up with Prince Harry as King and Meagain as Queen or Consort or whatever they would call her.
https://www.dailymail.co.uk/news/article-7383097/Inside-Prince-Harry-Meghan-Markles-private-jet.html
Inside Prince Harry and Meghan Markle’s private jet: Photos reveals lavish interior of luxury 12-seater Cessna used by eco-preaching Royal couple
You are correct. William should travel separately from his children.